This invention relates to the preparation of 1,1,2,3-tetrachloropropene and, more particularly, to novel methods for such preparation involving allylic rearrangement of 2,3,3,3,-tetrachloropropene or dehydrochlorination of 1,1,1,2,3-pentachloropropane.
1,1,2,3-tetrachloropropene ("Tetra") is an important chemical intermediate useful, for example, in the preparation of the herbicide trichloroallyl diisopropyl thiocarbamate, commonly referred to as "triallate". Conventionally, Tetra is produced by dehydrochlorination of 1,1,2,2,3-pentachloropropane that is produced in turn by chlorination of 1,2,3-trichloropropene. While this process provides a generally satisfactory technical route, the cost of producing the tetrachloropropene depends upon the cost of the trichloropropene raw material.
Smith U.S. Pat. No. 3,926,758 describes an alternative route to 1,1,2,3-tetrachloropropene in which 1,2,3-trichloropropane is chlorinated in an open vessel exposed to u.v. light to produce a mix of chlorinated products containing 20% to 60% by weight unreacted 1,2,3-trichloropropane. The chlorinator effluent is separated into five fractions, one of which contains 1,1,1,2,3- and 1,1,2,2,3-pentachloropropanes. Another fraction containing 1,1,2,3-tetrachloropropane is dehydrochlorinated and then rechlorinated to produce a further fraction containing 1,1,1,2,3- and 1,1,2,2,3-pentachloropropanes. These two pentachloropropane fractions are mixed and subjected to dehydrochlorination to provide a mix of 1,1,2,3- and 2,3,3,3-tetrachloropropenes which is fed to an isomerizer packed with siliceous granules in which the 2,3,3,3-isomer is converted to the 1,1,2,3-isomer.
U.S.S.R. Inventor's Certificate 899,523 describes a somewhat modified process in which 1,2,3-trichloropropane is chlorinated to produce tetrachloropropanes; 1,1,2,3- and 1,2,2,3-tetrachloropropanes are extracted from the reaction mixture and further chlorinated in the presence of dimethylformamide as an initiator to produce pentachloropropanes; 1,1,1,2,3- and 1,1,2,2,3-pentachloropropanes are extracted from the pentachloropropane mixture and dehydrochlorinated to produce a mixture of 1,1,2,3- and 2,3,3,3-tetrachloropropenes; and the latter mixture is boiled in the presence of aluminum oxide (attapulgite) to isomerize the 2,3,3,3- to the 1,1,2,3- isomer. An overall yield of 48.19% is reported. The reference describes as prior art a process very close to that of Smith.
An earlier reference by Haszeldine, "Fluoroolefins. Part II. Synthesis and Reaction of Some 3,3,3-Trihalogenopropenes" Journal of the Chemical Society [1953]pp. 3371-3378, describes a plethora of reactions of products derived from 1,1,1,3-tetrachloropropane. The reference describes preparation of this intermediate by reaction of carbon tetrachloride with ethylene in the presence of benzoyl peroxide. Among the numerous syntheses carried out by Haszeldine with 1,1,1,3-tetrachloropropane as the starting material are: dehydrochlorination of this starting material with 10% ethanolic potassium hydroxide to produce a mixture of 3,3,3- and 1,1,3-trichloropropene; isomerization of 3,3,3-trichloropropene to 1,1,3-trichloropropene using a variety of allylic rearrangement catalysts including antimony fluoride, concentrated hydrochloric acid, concentrated sulfuric acid, aluminum chloride, ferric chloride, ethanolic KOH and anhydrous hydrogen fluoride; chloroination of 1,1,3-trichloropropene in the presence of light to produce 1,1,1,2,3-pentachloropropane; chlorination of 3,3,3-trichloropropene to produce 1,1,1,2,3-pentachloropropane; dehydrochlorination of 1,1,1,2,3-pentachloropropane with ethanolic potassium hydroxide to produce a mixture of 2,3,3,3-tetrachloropropene and 1,1,2,3-tetrachloropropene; separation of 2,3,3,3-tetrachloropropene from 1,1,2,3-tetrachloropropene by distillation; and isomerization of 2,3,3,3-tetrachloropropene in the presence of aluminum chloride to produce 1,1,2,3-tetrachloropropene in 51% yield. Alternatively, Haszeldine discloses thermal isomerization of 2,3,3,3-tetrachloropropene to 1,1,2,3-tetrachloropropene at 180.degree. C. in 45% yield. Based on the yields reported by Haszeldine for the above described series of steps, the overall yield obtained with his syntheses can be computed as 41.8% based on 1,1,1,3-tetrachloropropane, 10.4% based on carbon tetrachloride.
Asahara et al., "The Telomerization of Ethylene and Carbon Tetrachloride", Kogyo Kagaku Zasshi 1971, 74(4), 703-5 discloses telomerization of ethylene and carbon tetrachloride at 130.degree. C. and at 60-70.times.10.sup.5 Pa (60-70 atmospheres) pressure in the presence of a triethyl phosphite-ferric chloride hexahydrate catalyst to produce 1,1,1,3-tetrachloropropane. Takamizawa et al. U.S. Pat. No. 4,243,607 describes an improvement in the Asahara process whereby higher yields of 1,1,1,3-tetrachloropropane are obtained by utilizing a catalyst system comprising a nitrile in addition to an iron salt and a trialkyl phosphite.
Japanese Kokai 74-66613 describes a process for producing 1,1,3-trichloropropene by dehydrochlorination of 1,1,1,3-tetrachloropropane using anhydrous FeCl.sub.3 as a catalyst. Reaction is carried out using 0.2 to 0.6 g FeCl.sub.3 per mole of 1,1,1,3-tetrachloropropane at a temperature of 80.degree. C. to 100.degree. C.
A need has remained in the art for improved processes for the synthesis of 1,1,2,3-tetrachloropropene, especially processes which provide this product in high yield using relatively inexpensive starting materials and which can be operated at modest manufacturing costs.